The present invention relates to an electronic digital taperule and, more particularly, to an actuating device for the electronic digital tape measure.
A conventional electronic digital tape measure was disclosed, for example, in U.S. Pat. Nos. 4,031,360 to Soule, and 4,316,081 to Washizuka. In the former reference, a measuring tape was formed of links fitted to each other, with each link perforated by a through hole, that is, the measuring tape had a considerably large volume and the housing of the tape measure was not compact. Furthermore, since the conventional measuring tape was not flexible per se, it was impossible to determine the length of curves such as the circumferential length of a tube or cylinder. The conventional measuring tape was also apt to damage fingers, etc. because of its sharp edges.
In order to eliminate such drawbacks in U.S. Pat. No. 4,031,360, U.S. Pat. No. 4,316,081 provides a compact electronic digital tape measure having an improved flexible measuring tape structure capable of measuring both the length of straight line and curves. In this patent, there is disclosed a flexible measuring tape constituted by allocating a number of magnetic balls in predetermined space from each other and by locating a number of non-magnetic balls to provide the space therebetween. The chain of the magnetic balls and the non-magnetic balls is buried within a flexible tape generally made from synthetic resin and the like. Due to the complicated special structure of the flexible tape, it is difficult to manufacture such a tape and the manufacturing cost is considerable high. U.S. Pat. No. 4,031,360 also provides a common flexible measuring tape which has no special structure similar to the above-mentioned flexible tape. An electronic actuating and detecting device comprising a photoelectric sensor, a rotatable disc having slits, a counter, a display and a pressure roller is provided within the housing and its arrangement is such that the detecting device may detect the measuring tape pulled out from the housing through said pressure roller and disc, and generate a series of signals to the counter to display the corresponding length of the tape in digit form through an electronic circuit. According to the above-said known digital tape measure, the disclosure relates to the basic arrangement and principle of the assembly only and does not account for a detail in constitution and relation in the components, especially, the actuating device which is very important to a tape measure. Therefore, there exists many problems in the manufacture or work-out of the known tape measure, and even in making the invention a practical use.